1. Technical Field
The present invention relates to an image forming apparatus which forms an image in continuous form paper.
2. Related Art
In the image forming apparatus in which the continuous form paper is used, tension of the continuous form paper is kept at a proper value in each portion of a conveyance path of the continuous form paper, particularly near a transfer unit which transfers a toner image formed in a photosensitive body to the continuous form paper. However, when the tension is fluctuated, sometimes poor print is generated, and conveyance failure such as paper jam is generated in the worst case. Particularly, in a full-color printer in which toner images having different colors formed in plural photosensitive bodies are superposed by sequentially transferring on the continuous form paper, it is necessary to suppress the tension fluctuation because higher accuracy is required for the conveyance of the continuous form paper.
Therefore, various configurations in which the tension is stabilized have been proposed.
A fixing device imparts thermal energy to fix an unfixed toner image to the continuous form paper. At this point, expansion and contraction are generated in the continuous form paper. Particularly the expansion and contraction occur remarkably in the case of a flash fixing method in which the unfixed toner image is fixed by flash light of a xenon lamp or the like. Thus, when the expansion and contraction are generated in fixing the unfixed toner image with the fixing device, the fluctuation in tension is generated in the continuous form paper, which results in the poor print and the conveyance failure.
In order to avoid such failures, it is necessary that the fluctuation in tension caused by the expansion and contraction of the continuous form paper in the fixing unit have no influence on the transfer unit located on the upstream side. Specifically, a drive roller which grips and conveys the continuous form paper while nipping the continuous form paper may be provided on the upstream side (between the transfer unit and the fixing unit) of the fixing unit, which allows the fluctuation in tension caused by the expansion and contraction of the continuous form paper in the fixing unit to be cut off. However, because the toner image on the continuous form paper on the upstream side (between the transfer unit and the fixing unit) of the fixing unit is the unfixed toner image, it is impossible to form the configuration in which the continuous form paper is gripped and conveyed while nipped. Therefore, it is impossible to provide the drive roller which grips and conveys the continuous form paper while nipping the continuous form paper on the upstream side of the fixing unit (between the transfer unit and the fixing unit).
That is, it is difficult that the fluctuation in tension caused by the expansion and contraction of the continuous form paper in the fixing unit has no influence on the transfer unit located on the upstream side.